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United States Patent |
5,707,486
|
Collins
|
January 13, 1998
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Plasma reactor using UHF/VHF and RF triode source, and process
Abstract
A plasma reactor preferably uses a split electrode which surrounds a plasma
dome region of the reactor, is driven by high frequency energy selected
from VHF and UHF and produces an electric field inside the electrode,
parallel to the wafer support electrode. A static axial magnetic field may
be used which is perpendicular to the electric field. The above apparatus
generates a high density, low energy plasma inside a vacuum chamber for
etching metals, dielectrics and semiconductor materials. Relatively lower
frequency, preferably RF frequency, auxiliary bias energy applied to the
wafer support cathode controls the cathode sheath voltage and controls the
ion energy independent of density. Various etch processes, deposition
processes and combined etch/deposition processes (for example,
sputter/facet deposition) are disclosed. The triode (VHF/UHF split
electrode plus RF wafer support electrode) provides processing of
sensitive devices without damage and without microloading, thus providing
increased yields.
Inventors:
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Collins; Kenneth S. (San Jose, CA)
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Assignee:
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Applied Materials, Inc. (Santa Clara, CA)
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Appl. No.:
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683125 |
Filed:
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July 16, 1996 |
Current U.S. Class: |
156/345.38; 156/345.45; 204/298.34; 216/67; 216/70 |
Intern'l Class: |
B44C 001/22; C03C 015/00; H01L 021/306 |
Field of Search: |
156/345,643.1,646.1
216/67,63,71
204/192.12,192.32,298.06,298.34
|
References Cited
U.S. Patent Documents
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4382100 | May., 1983 | Holland | 427/38.
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4464223 | Aug., 1984 | Gorin | 204/298.
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4572759 | Feb., 1986 | Benzing | 156/345.
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4579618 | Apr., 1986 | Celestino et al. | 204/298.
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4585516 | Apr., 1986 | Corn et al. | 204/298.
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4585668 | Apr., 1986 | Asmussen et al. | 427/38.
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4617079 | Oct., 1986 | Tracy et al. | 204/192.
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4622094 | Nov., 1986 | Otsubo | 156/627.
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4755345 | Jul., 1988 | Baity, Jr. et al. | 376/123.
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4788473 | Nov., 1988 | Mori et al. | 315/39.
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4792732 | Dec., 1988 | O'Loughlin | 315/334.
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4810935 | Mar., 1989 | Boswell | 315/111.
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4824546 | Apr., 1989 | Ohmi | 204/192.
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4828369 | May., 1989 | Hotomi | 350/357.
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4829215 | May., 1989 | Kim et al. | 315/111.
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4842683 | Jun., 1989 | Cheng et al. | 156/345.
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4849675 | Jul., 1989 | Muller | 315/111.
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4859908 | Aug., 1989 | Yoshida et al. | 315/111.
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4863549 | Sep., 1989 | Grunwald | 204/298.
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4877999 | Oct., 1989 | Knapp et al. | 315/248.
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4889588 | Dec., 1989 | Fior | 204/298.
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4906898 | Mar., 1990 | Moisan | 315/39.
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4908492 | Mar., 1990 | Okamoto et al. | 219/121.
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4918031 | Apr., 1990 | Flamm et al. | 437/225.
|
4948458 | Aug., 1990 | Ogle | 156/643.
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4950377 | Aug., 1990 | Huebner | 204/298.
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4950956 | Aug., 1990 | Asamaki et al. | 315/111.
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4990229 | Feb., 1991 | Campbell et al. | 204/298.
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5022979 | Jun., 1991 | Hijikata et al. | 204/298.
|
5028847 | Jul., 1991 | Greb et al. | 315/248.
|
5064522 | Nov., 1991 | Wellerdieck | 204/298.
|
5110438 | May., 1992 | Ohmi et al. | 204/298.
|
Foreign Patent Documents |
309648 | ., 0000 | EP | .
|
334648 | ., 0000 | EP | .
|
0058820 | Sep., 1982 | EP.
| |
0334638 | Sep., 1989 | EP.
| |
61-64124 | ., 0000 | JP | .
|
Other References
Boyer, "Hula-Hoop Antennas": A Coming Trend?,Electronics, Jan. 11, 1963,
pp. 44-46.
Coburn et al, "Positive-Ion Bombardment of Substrates in RF Diode Glow
Discharge Sputtering", J. Appl. Phys., vol. 43, 1972, p. 4965.
Keller et al, "A Dual Frequency, Tri-Electrode System For Etching
Polysilicon", Mat. Res. Soc. Symp. Proc., vol. 38, 1985, pp. 243-246.
Martin et al, "RF Bias to Control Stress and Hydrogen in PECVD Nitride",
Proceedings of the IEEE VLSI Multilevel Interconnection Conference, Jun.
13-14, 1988, pp. 286-292.
Cook et al, "Application of a Low-Pressure Radio Frequency Discharge Source
to Polysylicon Gate Etching", J. Vac. Sci. Technol. B, vol. 8, No. 1, Feb.
1990, pp. 1-4.
Yoshida et al, "Fabrication of a-Si:H TFT's by a Large Area Ion Doping
Technique", Extended Abstracts of the 22nd Conference on Solid State
Devices and Materials, Aug. 22-24, 1990, pp. 1197-1198.
Nutley, "Single Wafer, Anisotropic Etching of Polysilicon with C12/SF6 and
Trielectrode Reactor Operation" (date and publication unknown).
Goto et al, "Development of Dual Excitation Plasma Equipment (DEPE) to
Minimize Wafer Surface Damage and Chamber Material Contamination" (date
and publication unknown).
|
Primary Examiner: Nguyen; Nam
Attorney, Agent or Firm: Sgarbossa; Peter J., Morris; Birgit E.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation of U.S. application Ser. No. 08/367,912 filed Jan.
3, 1995, abandoned which is a continuation of U.S. application Ser. No.
08/128,033 filed Sep. 28, 1993 abandoned, which is a continuation of U.S.
application Ser. No. 07/644,004, now abandoned, which application is a
continuation-in-part of, commonly assigned U.S. patent application, Ser.
No. 626,050, entitled PLASMA REACTOR USING UHF/VHF RESONANT ANTENNA
SOURCE, AND PROCESSES, filed Dec. 7, 1990, in the name of inventor Collins
(AMAT file no. 252-1), now abandoned as a continuation-in-part of commonly
assigned U.S. patent application, Ser. No. 624,740, entitled PLASMA
REACTOR USING UHF/VHF RESONANT ANTENNA SOURCE, AND METHOD PROCESSES, FILED
Dec. 3, 1990, in the name of the inventor Collins (AMAT file no. 252), as
a continuation-in-part of, now abandoned, commonly assigned U.S. patent
application, Ser. No. 559,947, entitled UHF/VHF REACTOR SYSTEM, filed Jul.
31, 1990, in the name of inventors Collins et al (AMAT file No. 151-1),
now issued as U.S. Pat. No. 5,210,466.
Claims
I claim:
1. A system for processing a workpiece comprising:
a vacuum processing chamber for the workpiece;
a chamber inlet for introducing process gas into the chamber;
a plurality of electrodes coupling AC electrical energy into the chamber to
generate a plasma in the gas, the electrodes comprising a first electrode
structure having two separate sections for defining a plasma-generating
electrical field, the field being concentrated within a region of the
chamber spaced from the workpiece, the field also being principally
oriented parallel to the workpiece for preventing ion acceleration from or
toward the workpiece, and a second electrode structure adapted to support
the workpiece and for modifying a sheath voltage associated with the
electrodes and plasma ion energy proximate the workpiece;
first source of AC electrical energy to the first electrode at a first
frequency within the range of about 50 MHz to about 800 MHz, and
a second source of AC electrical energy to the second electrode at a second
frequency within the range of about 0.1 MHz up to but below about 50 MHz,
thereby controlling the sheath voltage and the plasma ion energy.
2. The system of claim 1, wherein:
the chamber includes a dielectric dome internally defining a section of the
chamber; the first electrode structure surrounds the chamber section
defined within the dome; the second electrode structure has a planar
surface proximate and parallel to the workpiece; and
the first electrode structure and the second electrode structure are
positioned for forming an electric field in the chamber parallel to and
spaced from the planar surface of the second electrode structure.
3. The system of claim 2, wherein the first electrode structure is located
on the interior of the dielectric dome and is covered on the inside of the
dielectric dome.
4. The system of 2, wherein the first electrode structure is formed on the
exterior of the dielectric dome.
5. The system of claim 1, wherein the first electrode structure comprises a
split electrode, the system further comprising means for feeding the gas
within the chamber from proximate the chamber inlet to proximate the
workpiece for transporting components of the plasma into contact with the
workpiece.
6. The system of claim 5,
wherein the chamber comprises an exhaust port for evacuating the chamber;
and
wherein said chamber inlet comprises:
said exhaust port which is located opposite the workpiece from the split
electrode; and
a plurality of gas inlet ports for admitting the gas into the chamber, the
inlet ports being spaced about the chamber proximate the split electrode
for producing gas flow toward the workpiece from the selected region of
the chamber.
7. The system of claim 5, wherein the split electrode comprises a pair of
approximately semicircular ring members.
8. The system of claim 7, wherein the ring members concentrically enclose
the chamber for concentrating the electric field within a right circular
cylinder that is perpendicular to the workpiece.
9. The system of claim 1, wherein said chamber comprises a first chamber
including said first electrode structure and a second chamber including
said second electrode structure and having a central opening in a wall
thereof, side walls of said first chamber substantially extending to said
central opening, whereby said first chamber substantially uninterruptibly
communicates with said second chamber.
10. A system for processing a workpiece in a plasma generated from a gas,
comprising:
a vacuum processing chamber for receiving the gas;
a support electrode for supporting the workpiece within the chamber;
a split electrode surrounding a volume of the chamber in parallel spaced
relation to the workpiece for capacitively coupling AC electrical energy
into the chamber to produce a plasma-inducing electrical field in a
selected region of the chamber spaced from the support electrode, to
prevent damage to the workpiece, and
a first power supply connected to the split electrode for supplying high
frequency AC energy having a frequency in the range of 50-800 MHz to the
split electrode and for controlling the power of the energy, to provide
selected plasma density and plasma ion current density; and
a second power supply for applying to the support electrode selected AC
electrical energy of lower frequency, in the range 0.1 MHz up to but below
50 MHz, than said capacitively coupled AC electrical energy, and for
controlling said selected AC electrical energy applied to the support
electrode to control a plasma sheath voltage at the support electrode and
an associated plasma ion energy.
11. The system of claim 10, further comprising means for applying to the
chamber a magnetic field oriented non-orthogonal to the electric field and
transverse to the support electrode, for controlling the location of the
plasma and extending the plasma downstream to the workpiece.
12. The system of claim 10, further comprising means for feeding the gas
within the chamber from proximate the selected region to proximate the
workpiece for transporting components of the plasma into contact with the
workpiece.
13. The system of claim 12, wherein the chamber comprises an exhaust port
for evacuating the chamber, and wherein the means for feeding the gas
comprises:
said exhaust port which is located opposite the workpiece from the split
electrode; and
a plurality of gas inlet ports for admitting the gas into the chamber, the
inlet ports being spaced about the chamber proximate the dielectric dome
for producing gas flow toward the workpiece from the selected regions of
the chamber.
14. A system for processing a workpiece according to claim 10 wherein said
chamber includes a dielectric dome inside the split electrode.
15. A process for generating a plasma, comprising:
supporting a workpiece on a supporting electrode within a vacuum chamber;
supplying gas to the vacuum chamber;
using a surrounding electrode structure having two separate sections
surrounding a volume of the vacuum chamber in relation to the workpiece,
capacitively coupling electrical energy at a first frequency of from
50-800 MHz into the chamber for generating a plasma from the gas for
processing one or more materials on the workpiece; and
controlling the power of the first frequency electrical energy;
applying RF energy to the supporting electrode at a second frequency of 0.1
up to but below 50 Mhz; and
controlling a power of the RF energy at said second frequency.
16. The process of claim 15, wherein a power delivered to the surrounding
electrode structure defines an ion flux density and the power delivered to
the supporting electrode defines a cathode sheath voltage, for directing
ions and controlling ion energy independently of the ion flux density.
17. The process of claim 15, wherein the plasma is generated within a
region of concentration of electrical energy at the first frequency, and
wherein the step of supplying the gas to the vacuum chamber comprises the
further step of feeding the gas within the chamber in a direction toward
the workpiece from proximate the region of first frequency energy
concentration.
18. A process for generating a plasma according to claim 15 wherein a first
power source is connected to the first frequency electrical energy and is
selected to control the plasma density.
19. A process for generating a plasma according to claim 15 wherein a
second power source is connected to the second frequency electrical energy
and is selected to control the sheath voltage at the supporting electrode.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to RF plasma processing reactors and, more
particularly, to an inventive plasma reactor which uses high frequency
(HF) and low frequency (LF) energy sources and associated electrodes for
coupling the HF and LF energy to the plasma.
2. Description of the Related Technology
The trend toward increasingly dense integrated geometries has resulted in
components and devices of very small geometry which are electrically
sensitive and susceptible to damage when subjected to wafer sheath
voltages as small as approximately 200-300volts due to energetic particle
bombardment or radiation. Unfortunately, such voltages are of smaller
magnitude than the voltages to which the circuit components are subjected
during standard integrated circuit fabrication processes.
Structures such as MOS capacitors and transistors fabricated for advanced
devices have very thin (thickness<200 Angstroms) gate oxides. These
devices may be damaged by charge-up, resulting in gate breakdown. This can
occur in a plasma process when neutralization of surface charge does not
occur, by non-uniform plasma potential/or density, or by large RF
displacement currents. Conductors such as interconnect lines may be
similarly damaged.
RF Systems
Consider first prior art semiconductor processing systems such as CVD
(chemical vapor deposition) and RIE (reactive ion etching) reactor
systems. These systems may use radio frequency energy at low frequencies
from about 10-500 Khz up to higher frequencies of about 13.56-40.68 Mhz.
Below about 1 Mhz, ions and electrons can be accelerated by the
oscillating electric field, and by any steady state electric field
developed in the plasma. At such relatively low frequencies, the electrode
sheath voltage produced at the wafers typically is up to one or more
kilovolts peak, which is much higher than the damage threshold of 200-300
volts. Above several Mhz, electrons are still able to follow the changing
electric field. More massive ions are not able to follow the changing
field, but are accelerated by steady state electric fields. In this
frequency range (and at practical gas pressures and power levels), steady
state sheath voltages are in the range of several hundred volts to 1,000
volts or more.
Magnetic Field-Enhancement
A favorite approach for decreasing the bias voltage in RF systems involves
applying a magnetic field to the plasma. This B field confines the
electrons to the region near the surface of the wafer and increases the
ion flux density and ion current and, thus, reduces the voltage and ion
energy requirements. By way of comparison, an exemplary non-magnetic RIE
process for etching silicon dioxide might use RF energy applied at 13.56
Mhz, an asymmetrical system of 10-15 liters volume, 50 millitorr pressure
and an anode area to wafer-support cathode area ratio of approximately
(8-10) to 1, and develop wafer (cathode) sheath voltage of approximately
800 volts. The application of a magnetic field of 60 gauss may decrease
the bias voltage approximately 25-30 percent, from 800 volts to about
500-600 volts, while increasing the etch rate by as much as about 50
percent.
However, the application of a stationary B field parallel to the wafer
develops an E.times.B ion/electron drift and an associated plasma density
gradient which is directed diametrically across the wafer. The plasma
gradient causes non-uniform etching, deposition and other film properties
across the wafer. The non-uniformities may be decreased by rotating the
magnetic field around the wafer, typically either by mechanical movement
of permanent magnets, or by using pairs of electromagnetic coils which are
driven in quadrature, 90 degrees out of phase, or by instantaneously
controlling the current in pairs of coils to step or otherwise move the
magnetic field at a controlled rate. However, although rotating the field
reduces the non-uniformity gradient, typically some degree of
non-uniformity remains.
Furthermore, it is difficult to pack coils and, in particular, to pack two
or more pairs of coils about a chamber and to achieve a compact system,
especially when using a Helmholtz coil configuration and/or a
multi-chamber system of individual magnetic-enhanced reactor chambers
surrounding a common loadlock.
A unique reactor system which has the capability to instantaneously and
selectively alter the magnetic field strength and direction, and which is
designed for use in compact multi-chamber reactor systems, is disclosed in
commonly assigned U.S. Pat. No. 4,842,683, issued Jun. 27, 1989, in the
name of inventors Cheng et al.
Microwave/ECR Systems
Microwave and microwave ECR (electron cylotron resonance) systems use
microwave energy of frequencies >800 MHz and, typically, frequencies of
2.45 GHz to excite the plasma. This technique produces a high density
plasma, but low particle energies which may be below the minimum reaction
threshold energy for many processes, such as the reactive ion etching of
silicon dioxide. To compensate, energy-enhancing low frequency electrical
power is coupled to the wafer support electrode and through the wafer to
the plasma. Thus, the probability of wafer damage is decreased relative to
previous systems.
Microwave and microwave ECR systems operated at practical power levels for
semiconductor wafer processing such as etch or CVD require large
waveguides for power transmission, and expensive tuners, directional
couplers, circulators, and dummy loads for operation. Additionally, to
satisfy the ECR condition for microwave ECR systems operated at the
commercially available 2.45 GHz, a magnetic field of 875 gauss is
necessary, requiring large electromagnets, large power and cooling
requirements.
Microwave and microwave ECR systems are not readily scalable. Hardware is
available for 2.45 GHz, because this frequency is used for microwave
ovens. 915 MHz systems are also available, although at higher cost.
Hardware is not readily or economically available for other frequencies.
As a consequence, to scale a 5-6 in. microwave system upward to
accommodate larger semiconductor wafers requires the use of higher modes
of operation. This scaling at a fixed frequency by operating at higher
modes requires very stringent process controls to avoid so-called mode
flipping to higher or lower order moads and resulting process changes.
Alternatively, scaling can be accomplished, for example, for a 5-6 in.
microwave cavity, by using a diverging magnetic field to spread out the
plasma flux over a larger area. However, this method reduces effective
power density and thus plasma density.
SUMMARY OF THE INVENTION
In one aspect, my invention which satisfies the above and other criteria is
embodied in a system for processing a workpiece in an enclosure defining a
vacuum processing chamber by introducing process gas into the chamber and
generating a plasma from the gas, comprising: electrode means for coupling
AC electrical energy into the chamber to generate a plasma in the gas; and
means for applying high frequency VHF/UHF electrical energy to the
electrode means for controlling the density of the plasma and the plasma
ion density.
In addition, my invention encompasses an embodiment wherein the electrode
means is adapted for applying relatively lower frequency AC electrical
energy to the electrode means for controlling the sheath voltage
associated with the electrode means and plasma ion energy. Preferably, the
frequency of the high frequency AC energy is within the range of about 50
MHz to about 800 MHz, and that of the relatively lower frequency AC energy
is within the range of about 0.1 MHz to about 50 MHz.
In another aspect, the electrode means comprises two electrode structures
for applying plasma generating AC electrical energy to the chamber, the
means for applying the high frequency AC electrical energy is connected to
one of the electrode structures and the means for applying the relatively
lower frequency AC electrical energy is connected to the other of the two
electrode structures.
In yet another aspect, the enclosure includes a dielectric window in one
surface thereof; the electrode means includes a wafer support electrode
within the chamber and a plate electrode on the dielectric window; the
means for applying the relatively low frequency AC energy is connected to
the wafer support electrode; the means for applying high frequency AC
energy is connected to the chamber enclosure; the plate electrode is at
system ground; and both means for applying AC electrical energy are
referenced to the plate electrode as ground, such that the electrodes form
an electric field in the chamber between the wafer support electrode and
the plate electrode.
In an alternative embodiment, the electrode means is a single electrode
structure located within the chamber and adapted for supporting a
workpiece, and both means for applying AC electrical energy to the
electrode means are connected to the single electrode structure.
In another alternative embodiment, the enclosure includes a dielectric
window in one surface thereof; the electrode means includes a wafer
support electrode within the chamber and a plate electrode on the
dielectric window; the means for applying high frequency AC electrical
energy is connected to the plate electrode; the means for applying the
relatively low frequency AC energy is connected to the wafer support
electrode; and both means for applying AC energy are referenced to the
chamber enclosure as ground, such that the electrodes form an electric
field in the chamber between the wafer support electrode and the plate
electrode.
In a presently preferred embodiment, the electrode means includes an
electrode located within the chamber and adapted for supporting a
workpiece thereon and an electrode structure surrounding the periphery of
the plasma chamber; the means for applying high frequency AC energy is
connected to the peripheral electrode structure; and the means for
applying relatively lower frequency AC energy is connected to the wafer
support electrode. Preferably, the enclosure includes a dielectric dome
internally defining a section of the chamber; the peripheral electrode
structure surrounds the chamber section defined within the dome; the
peripheral electrode structure and the wafer support electrode are
positioned for forming an electric field in the chamber parallel to the
wafer support electrode; and the surrounding electrode structure comprises
separate sections and, in combination with the means for applying the high
frequency AC electrical energy, provides a differentially driven,
ungrounded, balanced drive arrangement for the electrode structure.
In still additional embodiments, the enclosure/chamber according to my
invention includes an integral transmission line structure adapted to
apply AC electrical energy of selected frequency from the external source
to the plasma chamber, comprising: the wafer support electrode; an outer
conductor surrounding the wafer support electrode; and an insulator
between the wafer support electrode and the outer conductor such that AC
energy applied to the transmission line structure is coupled along the
wafer support electrode for controlling the cathode sheath voltage. Also,
the high frequency AC electrical energy can be coupled to the electrode
means via a matching network. In addition, a biased grid can be
incorporated for extracting a stream of charged ions or electrons from the
plasma, and a neutralization grid can be located spaced from the
extraction grid for extracting a stream of excited neutrals and free
radicals.
Other, preferred aspects include a reflector positioned surrounding the
electrode means, for preventing radiation of the AC energy into free
space.
Magnetic enhancement may be supplied by peripheral permanent or
electromagnet arrangements which apply a controlled static magnetic field
orthogonal to the plane of the electric field of the surrounding
electrode, selected from uniform, diverging and magnetic mirror
configurations, for controlling the location of and the transport of the
plasma downstream relative to the wafer. Also, magnets may be mounted
around the chamber for applying a multipolar cusp field to the chamber in
the vicinity of the wafer for confining the plasma to the wafer region
while substantially eliminating the magnetic field across the wafer. In
addition, a magnetic shunt may be positioned surrounding the wafer and the
wafer support electrode for diverting any magnetic field from the wafer
support electrode.
The system construction permits scaling of its size by selecting the
frequency of operation.
In another aspect, my invention is embodied in the construction and
operation of a plasma processing reactor, comprising: a housing including
a dielectric dome defining a plasma chamber therein; electrode means
within the plasma chamber for supporting a semiconductor wafer; a gas
inlet manifold in the housing for supplying reactant gas to the plasma
chamber; vacuum pumping means communicating with the plasma chamber for
maintaining a vacuum therein; and a high frequency energy source
comprising a split electrode surrounding the dome for capacitively
coupling high frequency energy of controlled power into the plasma chamber
for generating a plasma therein of controlled density and controlled ion
flux density. As mentioned, this system may incorporate various preferred
and alternative features, including, preferably, an energy source for
coupling lower frequency energy of controlled power into the chamber for
controlling the sheath voltage at the wafer support. The bias frequency is
selected to control voltage; bias power is selected/varied, to control
sheath voltage and ion energy.
In other, process aspects, my invention is embodied in a process for
coupling high frequency energy into a processing chamber within a vacuum
enclosure, preferably via a split electrode surrounding a dielectric dome
portion of the enclosure, for generating a plasma within the chamber to
effect fabrication of materials selected from etching of materials,
deposition of materials, simultaneous etching and deposition of materials
and/or sequential etching and deposition of materials. Alternatively, the
high frequency power is applied via a plate electrode formed on a
dielectric window in the enclosure. The process also involves controlling
the high frequency power to control plasma density and ion flux density.
Preferably, the object undergoing fabrication is supported on an electrode
and relatively lower frequency AC power is applied to the electrode for
independently controlling the associated sheath voltage and the ion
energy, with respect to plasma density and ion flux density.
Specific process aspects include but are not limited to etching oxide,
including etching contact holes in oxide formed over polysilicon
(polycrystalline silicon) and etching via holes in oxide formed over
aluminum; so-called "light" etching of silicon oxide and polysilicon; high
rate isotropic and anisotropic oxide etching; etching polysilicon
conductors such as gates; photoresist stripping; anisotropic etching of
single crystal silicon; anisotropic photoresist etching; low pressure
plasma deposition of nitride and oxynitride; high pressure isotropic
conformal deposition of oxide, oxynitride and nitride; etching metals,
such as aluminum and titanium, and compounds and alloys thereof; and
sputter facet deposition, locally and globally, and with planarization.
BRIEF DESCRIPTION OF THE DRAWING
The above and other aspects of my invention are described with respect to
the drawing in which:
FIG. 1 schematically depicts an RF reactor system in accordance with my
present invention;
FIGS. 2, 3 and 4 schematically depict systems incorporating alternative
electrode configurations;
FIG. 5 is a block diagram of a presently preferred power control system;
FIG. 6 depicts a representative integrated circuit via hole;
FIG. 7 depicts the via hole of FIG. 6 after application of a widening
sequence in accordance with my invention;
FIGS. 8A-8D depict various magnetic enhancement fields;
FIG. 9 is an electrical schematic of a presently preferred matching network
for the preferred, differentially driven, ungrounded, balanced split
electrode arrangement of FIG. 1.;
FIG. 10 is a schematic physical equivalent of FIG. 9; and
FIG. 11 is a simplified schematic depiction of a motor control circuit for
the network of FIGS. 9 and 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
1. Overall System
FIG. 1 is a schematic sectional view of a plasma reactor chamber system 10
which uses a plural (two or more) electrode plasma source arrangement, a
magnetically-enhanced plasma source arrangement and other aspects of my
present invention. The exemplary chamber is a modification of that
depicted in my incorporated U.S. Pat. No. 5,210,466, which includes an
integral transmission line structure. The salient features of my invention
are applicable generally to plasma reactor chambers. Furthermore, it will
be understood by those of skill in the art and from the description below
that various features of the invention which cooperatively enhance the
performance of the reactor system may be used separately or may be
selectively omitted from the system. For example, the process conditions
provided by the plural (two or more) electrode plasma source arrangement
frequently eliminate any need for magnetic enhancement.
The exemplary system 10 includes a vacuum chamber housing or enclosure 11,
formed of anodized aluminum or other suitable material, having sidewalls
12 and top and bottom walls 13 and 14. Anodized aluminum is preferred
because it suppresses arcing and sputtering. However, other materials such
as bare aluminum and process-compatible polymers or quartz or ceramic
liners can be used. The chamber can be heated or cooled for process
performance. Top wall or ceiling 13 has a central opening 15 between a
lower chamber section 16A defined between walls 12--12 and an upper
chamber section 16B defined by a dielectric dome 17. The dome preferably
is quartz but can be made of several dielectric materials, including
alumina and alpha-alumina (sapphire). The dome may be heated or cooled as
required for process performance. A fluid or gas heat transfer medium may
be used, or heating elements may be used to heat the dome directly.
Various vacuum seals 18 such as O-rings are interposed between the various
mating surfaces to maintain vacuum-tight enclosure. The interior of the
chamber housing 11 (chamber 16) is evacuated via a throttle valve 19
(which regulates pressure independent of flow rate) in a vacuum line 21
which connects to a vacuum pumping system (not shown).
Reactant gases are supplied to the chamber 11, as indicated schematically
at 22, typically from one or more sources of pressurized gas via a
computer-controlled flow controller (not shown) and enter the internal
vacuum processing chamber 16 through ring gas manifold 23, which is
mounted on the inside of or integral with, top wall 13. The manifold 23
preferably supplies etching gas and/or deposition gas at a slight upward
angle to the chambers/chamber sections 16B and 16A for developing an
etching and/or deposition plasma upon application of high frequency RF
energy. Gases may be brought in directly via the process chamber instead
of, or in addition to, through the manifold. For example, it may be
desired to bring an inert gas or other gas into the manifold 23, and bring
other reactant gases in via a lower manifold or gas inlet (not shown) in
the process chamber below.
The high frequency (HF) energy such as, preferably, VHF/UHF energy of
frequency 50 to 800 MHz is applied by a substantially closed, split
electrode structure 25 comprising a pair of generally semi-circular band
electrodes 26--26, which surround the dome 17 and are powered by a high
frequency (HF) source 27, and effect plasma excitation in the chamber 16
by capacitive coupling via the dielectric dome 17. This contrasts with
conventional RF system arrangements, in which the RF power is applied
between two electrodes, typically the wafer support electrode 32C, the
upper surface of which supports wafer 5, and a second electrode which is
defined by the sidewalls 12, top wall 13 and/or manifold 23 of the reactor
chamber.
Preferably, the HF AC source 27 is coupled to the electrode 25 by a
suitable matching network 28 via a transmission line structure having twin
leads 77--77 coupled to the band electrodes 26--26 to provide a
differentially driven, balanced, ungrounded drive arrangement. This system
is shown in FIGS. 9-11 and described more fully in .sctn.3 below.
Preferably, the gas flow from the upper chamber section 16B is downward
toward the wafer 5 and is then pumped radially outward from the wafer. To
this end, an annular vacuum manifold 33 is defined about cathode
transmission line structure 32, between chamber wall 12 on one side and
the outer transmission line conductor 320 on the other, and between the
chamber bottom wall 14 on the bottom and a conductive pumping screen 29 on
the top. The manifold screen 29 is interposed between the vacuum manifold
33 and the plasma chamber 16A and provides a conductive electrical path
between chamber walls 12 and the outer conductor 320 of the transmission
line structure 32. The manifold 33 defines an annular pumping channel for
implementing uniform radial pumping of exhaust gases from the periphery of
wafer 5. The exhaust manifold 33 communicates into the exhaust gas system
line 21 via one or more apertures 31 in the bottom wall 14. The overall
gas flow is along path 22 into the inlet manifold 23, along path 24 into
the upper (and)lower chamber section, along path 34 from the upper chamber
section 16B toward wafer 5, along path 36 radially outwardly from the
peripheral edge of the wafer and through screen 29 into the gas outlet
manifold 33, and along path 37 from the exhaust manifold 33 to the exhaust
system 21.
The split electrode structure 25 is positioned adjacent the dome 17 and the
plasma chamber 16B for coupling the relatively high frequency (HF) energy
into the chamber and forming a changing electric field between the two
band electrodes in a generally right cylinder volume therein parallel to
the top surface of the wafer support electrode 32C and the wafer 5
thereon. The changing electrical fields energize the process gas and thus
form a plasma in chamber 16 (numeral 16 collectively designates the
chamber 16A and 16B and the plasma therein) characterized by relatively
high density and low energy ions. The plasma is generated in the dome
concentrated in the above-mentioned right cylindrical volume defined by
the electrode 25 and active species including ions, electrons, free
radicals and excited neutrals move downstream toward the wafer by
diffusion and by bulk flow due to the prevailing gas flow described
herein. Also, an appropriate magnetic field can be used to extract ions
and electrons toward the wafer as described below. Optionally, but
preferably, a low frequency bias energy input arrangement 41 comprising a
source 42 and a bias matching network 43 couples relatively low frequency
(LF) RF energy to the wafer support electrode 32C for selectively
increasing the plasma sheath voltage at the wafer and thus selectively
increasing the ion energy at the wafer. Preferably, the LF energy is
within the range of about 0.1 MHz to about 50 MHz.
A reflector 44 which essentially is an open-bottom box encloses the split
electrode 25 at the top and sides but not at the bottom. The reflector
prevents radiation of the HF energy into free space and thereby
concentrates the radiation and dissipation of the power in the plasma to
enhance efficiency.
As described in greater detail below, optionally, one or more
electromagnets 47--47 or permanent magnets are mounted adjacent the
chamber enclosure 11 for providing a static shaped-magnetic field for
enhancing the density of the plasma at the wafer 5.
In short, my invention uses relatively high frequency electrical energy,
typically 50 MHz to 800 MHz (high frequency relative to the optional bias
energy but typically much lower than microwave or microwave-ecr
frequencies), to produce directed, generally horizontal fields inside a
vacuum chamber for generating a plasma characterized by high density and
relatively low energy, without coupling potentially damaging HF energy
through the wafer 5. In the preferred downstream plasma source arrangement
illustrated in FIG. 1, the energy is fully absorbed remote from the wafer,
with high plasma density, ensuring that the energy does not propagate to
the wafer and thus minimizing the probability of damage. Selectively, and
optionally, relatively low frequency (LF) auxiliary AC bias energy is
applied to the wafer support electrode 32C for increasing the wafer sheath
voltage and, thus, the ion energy as required. The (1) HF energy and (2)
LF energy independently control (1) plasma density and ion density and (2)
sheath voltage and ion energy.
The frequency of the system may be varied within the range 50 to 800 MHz to
permit scaling the diameter of chamber 16B over the range 32 in. to 2 in.
In particular, the system can be scaled upward to accommodate the
increasingly large diameter wafers favored by the semiconductor industry,
without changing the electromagnetic mode, by the simple expedient of
decreasing the frequency within the described range and retaining low mode
operation, thus avoiding the possibility of mode flipping and process
changes which are associated with increasing the mode of operation.
Because the high frequency of the source 27 driving the split electrode
structure 25 is nonetheless much lower than the frequencies used in
microwave or microwave-ECR applications, the optional smaller magnets
operated at lower DC current by less expensive power supplies can be used,
with associated smaller heat loads. In addition, as is obvious from the
above discussion, a twin lead transmission line can be used instead of
wave guides. In addition, the plasma non-uniformities caused by the
E.times.B electron drift in other magnetic-enhanced or assisted systems
are absent here, because the applied magnetic fields (both the magnetic
component of the HF field applied via the electrode 25 and any static
axial magnetic field applied by magnets 47), are substantially parallel to
the electric field at the cathode 32C. Thus, there is no E.times.B drift
in the system.
A magnetic shunt path formed with a high permeability material may be used
to allow a B field in the source (upper chamber 16A) but not at the wafer.
Optionally, permanent or electromagnets can be placed in a multi-polar
arrangement around the lower chamber 16A, typically in an alternating pole
north-south-north-south . . . north-south arrangement, to generate a
multi-cusp magnetic mirror at the chamber walls. The magnets may be
vertical bar magnets or preferably horizontal ring magnets, for example.
Such magnets may be used to reduce electron losses to the walls, thus
enhancing plasma density, without subjecting the wafer to magnetic fields.
2. Magnetic Enhancement
As mentioned above, one or more (preferably, at least two) permanent or
electromagnets 47--47 define a static, generally axial magnetic field
orthogonal to and through the plane of the of the E field of the split
electrode 25. Preferably, one of three field-types is used: uniform,
divergent or magnetic mirror.
Referring to FIG. 8A, a homogeneous, axial uniform magnetic field 81
applied orthogonally to the wafer 5 restricts the motion of the electrons
to the walls. Because of the inability of ions to follow high frequency
field variations, the ions follow the electron deficiency, and are
concentrated in the plasma over the wafer. For maximum efficiency, this
and other static magnetic fields can be tuned to resonance with the high
frequency electromagnetic field: .omega.=2.pi.F=Be/m, where B is the
magnetic flux density and e and m are the electron charge and mass,
respectively.
An axially divergent field 82 is depicted schematically in FIG. 8B. By the
conservation of magnetic moment, the axial gradient of the magnetic field
converts circular translational energy to axial translational energy and
tends to drive the electrons and ions from the stronger field regions to
the weaker regions thereof. Diverging magnetic fields can be used to push
the electrons and ions from the plasma generating regions and to
concentrate the plasma at the wafer.
Referring to FIGS. 8C and 8D, there are shown, respectively, a bulging or
aiding magnetic field 83 (FIG. 8C) and a cusp-shaped or opposing field 84
(FIG. 8D). The effect of each of these so-called "magnetic mirror" fields
is similar to that of the axially divergent field: charged particles are
driven from the relatively strong field regions (at the ends here) toward
the relatively weak central region.
Selectively positioning the magnet(s) and selecting and varying the
strength of the fields provided by the single magnet or cooperating
magnets shapes the associated uniform, diverging, or magnetic mirror field
in controlled fashion to increase the density of the plasma at the wafer.
For magnetic mirror fields, the preferred wafer position for maximum
plasma density enhancement is closely adjacent to or at the bulge or cusp,
to provide maximum plasma density enhancement.
It may be desired to utilize an axial magnetic field at the plane of the
split electrode 25 to enhance plasma generation, but to eliminate the
magnetic field at the wafer 5. An annular disk of high magnetic
permeability materials (such as nickel or steel for soft iron) may be
interposed below the magnet(s) and plane of the split electrode 25 but
above the wafer 5. Optionally, multipolar confinement may be used in the
lower chamber region by defining ring or bar magnets in an alternating
pole arrangement.
3. Split Electrode Matching Network 28
To implement the split electrode embodiment depicted in FIG. 1 a matching
network is required to match the plasma load impedance presented to the
split electrode 25 and to the generator 27. In addition, it is desired to
drive the split electrode 25 differentially, in an ungrounded, balanced
(with respect to ground) fashion. Driving the electrodes in this manner
produces the most uniform plasma, and minimum particle energy.
The preferred matching network 28 is a modified embodiment of the matching
network described in above-mentioned co-pending, commonly assigned U.S.
Pat. No. 5,210,466 the disclosure of which patent is hereby incorporated
by reference. Referring to FIGS. 9 and 10, in addition to FIG. 1, the
presently preferred matching network 28 is an L-network comprising a shunt
capacitor C.sub.1 coupled from the input of the matching network to ground
and a series capacitor C.sub.2 coupled from the input of the matching
network to the output of the matching network, which ties directly to the
output transmission line section 70.
It should be noted that the matching network configuration depicted in
FIGS. 9 and 10 applies for a typical source output resistive impedance of
50 ohms and the typical plasma 16 resistive impedance component of 1 to 50
ohms and, more generally, when the source output resistance component is
greater than the load resistance component. Were the resistive part of the
plasma load impedance Z.sub.1 to exceed the output resistive impedance of
the source, the input and the output connections for the matching network
would be reversed.
Capacitors C.sub.1 and C.sub.2 are air capacitors which comprise fixed and
movable conductor plates, typically formed of copper or silver plated
cooper sheets. The fixed plate 58 of capacitor C.sub.1 is the case or
housing 51 of the matching network 28, which is connected to ground.
Referring also to FIG. 11, plate 57 is connected to the input 50 from the
power supply 27 and is movable along path 62 by motor M.sub.1 under the
control of the system controller 500, based upon the real time Z.sub.in or
reflected power. This input is used in controlling the plate separation
and, thus, the capacitance of the capacitors in a well-known manner. A
sheet 61 of Teflon.TM. or other suitable low loss, high dielectric
strength material is interposed between the capacitor plates 57 and 58 to
prevent arcing. Please note, as indicated schematically in FIG. 11, the
computer 500 (or a separate computer) is conveniently used to control the
operation of the power supply 27 and to select a proper frequency within
the range of interest and thereby select the desired voltage and power
combination for a given process.
Similarly-constructed series capacitor C.sub.2 comprises an insulative,
anti-arcing sheet 59 of material such as Teflon.TM., a leg 56 which is
connected to the input 50 and is movable by motor M.sub.2, in the manner
of capacitor C.sub.1, along path 63 to vary the capacitance of C.sub.2. A
fixed leg 55 is connected to the matching network's output 52, which
illustratively comprises a clip 54 which engages the downward-extending
conductor post or conductor 53. The conductor 53 is also part of the balun
output section 70. Post 53 is extended to add inductance as indicated at
L.sub.1, of FIG. 9.
The balun 70 converts the grounded match output to a balanced, differential
ungrounded output. A 1:1 balun is used. The tri-axial, electrically
quarter wave output section 70 comprised of center conductor (post) 53,
outer conductor 73, shield 72 and dielectric 74 and 75 is used to isolate
the split electrode 25 from ground by presenting a high impedance to any
ground current. Balun 70 is terminated via split conductor 76,
specifically the two leads 77--77 thereof, which connect to the individual
conductors 26--26 of the split electrode 25.
4. Transmission Line Structure 32
As described in detail in my incorporated U.S. Pat. No. 5,210,466, proper
coaxial/transmission line design requires both a feed via a low
characteristic impedance, short transmission line from the matching
network to the wafer and a return path along the transmission line. This
design requirement is satisfied by the integral transmission line
structure 32 depicted in FIG. 1 which comprises the cathode 32C,
concentric annular conductor 320, and a non-porous low loss insulator 32I
which surrounds the cathode 32C and insulates the cathode from the
concentric annular conductor 320 and displaces process gases which
otherwise might break down. For example, Teflon.TM. or quartz materials
are preferred because they have high dielectric strength, low dielectric
constant and low loss. The input side of this structure is connected to
the matching network in a manner described below. The insulated cathode
32C and outer conductor 320 provide separate current paths between the
matching network 43 and the plasma 16. One reversible current path 41 is
from the matching network along the outer periphery of the cathode 32C to
the plasma sheath at the chamber (electrode) surface. The second
reversible path 42 is from the plasma 16 along the upper inside section of
chamber walls 12 then along the conductive exhaust manifold screen 29 and
via the inside of the outer conductor 320 to the matching network. Please
note, the exhaust manifold screen 29 is part of the uniform radial gas
pumping system, and the return path for the RF current.
During application of alternating current energy, the RF current path
alternates between the directions shown and the reverse directions. Due to
the co-axial cable type of construction of the transmission line structure
32 and, more specifically, due to the higher internal impedance of the
cathode 32C (relative to the outside thereof) and the higher impedance
toward the outer surface of the conductor 320 (relative to the inner
surface thereof), the RF current is forced to the outer surface of the
cathode 32C and to the inner surface of the outer conductor 320, in the
manner of a co-axial transmission line. Skin effect concentrates the RF
current near the surfaces of the transmission line, reducing the effective
cross-section of the current path. The use of large wafers, for example,
wafers 4-8 inches in diameter and the commensurately large diameter
cathode 32C and large diameter outer conductor 320 provide large effective
cross-section, low impedance current paths along the transmission line
structure.
Also, if the co-axial-type transmission line structure 32 were terminated
in a pure resistance equal to its characteristic impedance Z.sub.0, then
the matching network would see the constant impedance Z.sub.0, independent
of the length of the transmission line. However, such is not the case
here, because the plasma is operating over a range of pressure and power,
and comprises different gases, which collectively vary the load impedance
Z.sub.1 that the plasma presents to the end of the transmission line 32.
Because the load Z.sub.1 is mismatched from the non-ideal (i.e.,
non-lossless) transmission line 32, standing waves present on the
transmission line will increase resistive, dielectric, etc., losses
between the transmission line and the matching network 31. Although the
matching network 43 can be used to eliminate any standing waves and
subsequent losses from the input of the matching network back to the
amplifier or power supply 30, the matching network, transmission line feed
32 and plasma inside the chamber comprise a resonant system that increase
the resistive, dielectric, etc., losses between the transmission line 32
and the matching network 43. In short, the load impedance Z.sub.1 will be
mismatched with losses, but losses are minimum when Z.sub.1
.about.Z.sub.0.
To diminish the losses due to the load mismatch, the co-axial-type
transmission line structure 32 is designed to have a characteristic
impedance Z.sub.0 that is best suited to the range of load impedances
associated with the plasma operation. Typically, for the above-described
operating parameters (example: wafer support electrode or bias frequency
range approximately 5-50 MHz) and materials of interest, the series
equivalent RC load impedance, Z.sub.1, presented by the plasma to the
transmission line will comprise a resistance within the approximate range
1 ohm to 30 ohms and a capacitance within the approximate range 50 pico
farads to perhaps 400 pico farads. Consequently, as the optimum, a
transmission line characteristic impedance Z.sub.0 is selected which is
centered within the load impedance range, i.e., is approximately 10 to 50
ohms.
It is necessary that the transmission line 32 be very short in order to
avoid transformation of the plasma impedance that the matching network
sees. Preferably, the transmission line is much less than a quarter
wavelength, .lambda./4, and, more preferably, is about (0.05 to 0.1)
.lambda.. More generally, if it is not possible to locate the matching
network at a distance much less than a quarter wavelength to the load,
advantage is taken of the half wavelength periodicity associated with the
impedance transformation by using a transmission line length equal to an
integral multiple n=1, 2, 3, etc., of a half wavelength (.lambda./2;
.lambda.; 3.lambda./2; etc.). More precisely, the preferred values are
.lambda./2 to (.lambda./2+0.05.lambda.); .lambda. to
(.lambda.+0.05.lambda.); 3.lambda./2 to (3 .lambda./2+0.05.lambda.);
etc.). Under such conditions, the matching network should not be located
at odd integrals of quarter wavelengths (.lambda./4, 3 .lambda./4, 5
.lambda./4), because a quarter wave section (or n .lambda./4 where n is
odd) transforms Z.sub.1 such that Z.sub.in =Z.sub.0 .sup.2 /Z.sub.1, where
Z.sub.1 is typically small, producing a very large Z.sub.IN. The matching
network then could not match to the plasma load and it would be very
difficult to couple power to the plasma without unacceptable system
resonance and power dissipation.
Also, for efficient coupling of power, the inside diameter (cross-section
dimension) of the return conductor 320 should not be significantly larger
than the outside diameter (cross-section dimension) of the center
conductor 32C.
In short, the chamber optionally but preferably incorporates a transmission
line structure that couples power from the matching network 43 to the
plasma 16. That transmission line structure (1) preferably is very short
compared to a quarter wavelength at the frequencies of interest or,
alternatively, is approximately equal to an integral half wavelength, to
prevent undesirable transformation of the plasma impedance; (2) has a
characteristic Z.sub.0 selected to suppress losses due to the presence of
standing waves on the line between the plasma and the matching network;
and (3) uses an outside conductor path cross-sectional dimension which is
not substantially larger than that of the center conductor.
5. Control System
The following descriptions are used here in reference to the control system
depicted in FIG. 5:
______________________________________
Psp: Power set point
P.sub.f :
Forward power Measured by directional
coupler located
at /inside power
supply
P.sub.r :
Reflected power Measured by directional
coupler located
at /inside power
supply
.linevert split.Z.linevert split.:
Magnitude of impedance
<phi: Phase of impedance
Tsp: Tune set point
Lsp: Load set point
Tfb: Tune feedback (measured)
Lfb: Load feedback (measured)
______________________________________
FIG. 5 is a block diagram of an exemplary system for controlling the
various components including the power supplies. Here, a system controller
500 is interfaced to surrounding (or split or top) electrode power supply
27, impedance bridge 502, matching network 28, electrode 25, bias power
supply 504, impedance bridge 505, matching network 43, and cathode 32C.
The process parameters top electrode power and DC bias, selected for ion
flux density and ion energy, are supplied as input to the controller 500.
Controller 500 may also control other parameters such as gas flow(s),
chamber pressure, electrode or wafer temperature, chamber temperature, and
others. The controller 500 may preset initial tune.sub.1 and load.sub.1
conditions by issuing signals on Tsp.sub.1 and Lsp.sub.1 lines connected
to matching network 28. The controller 500 may also preset initial
tune.sub.2 and load.sub.2 conditions by issuing signals on Tsp.sub.2 and
Lsp.sub.2 lines connected to the matching network 43. Typically, these
conditions are selected to optimize plasma initiation (gas breakdown).
Power may be applied first to either the electrode 25 or to the cathode
32, or it may be applied simultaneously to both. The controller issues
power set points on Psp.sub.1 line to power supply 27 and on Psp.sub.2
line to bias power supply 504 simultaneously or sequentially (in either
order).
Avalanche breakdown occurs rapidly in the gas, generating a plasma.
Controller 500 monitors forward power (P.sub.f1) and reflected power
(P.sub.r1) to/from the electrode 25, and monitors forward power (P.sub.f2)
and reflected power (P.sub.r2) to/from the cathode 32. DC bias (cathode to
anode DC voltage) is also monitored as shown by controller 500. Controller
500 adjusts the electrode tune.sub.1 and load.sub.1 parameters by issuing
set points on lines Tsp.sub.1 and Lsp.sub.1, based on either (a) forward
power P.sub.f1 and reflected power P.sub.r1, or (b) impedance magnitude
.linevert split.Z.sub.1 .linevert split. and impedance phase <phi.sub.1.
Bridge 502 furnishes impedance magnitude and phase angle information to
the controller. The electrode 25 is matched when reflected power P.sub.r1
is substantially zero and when the impedance (magnitude and phase
.linevert split.Z.sub.1 .linevert split.<phi) is the complex conjugate of
the top electrode power supply output impedance. (The zero reflected power
condition and the conjugate impedance condition occur simultaneously, so
either reflected power may be minimized or impedances may be matched, with
the same result. Alternatively, VSWR (voltage standing wave ratio) or
reflection coefficient may be minimized. Controller 500 adjusts the
cathode 32 and the matching network 43 tune.sub.2 and load.sub.2
parameters by issuing set points on the Tsp.sub.2 and Lsp.sub.2 lines,
based on either (a) forward power P.sub.f2 and reflected power P.sub.r2 or
(b) impedance magnitude .linevert split.Z.sub.2 .linevert split. and
impedance phase <phi.sub.2. Bridge 505 furnishes impedance magnitude
.linevert split.Z.sub.2 .linevert split. and phase <phi.sub.2 information
to the controller 500. Matching occurs when, similarly to electrode
matching, reflected power P.sub.r2 is essentially zero, and when impedance
(magnitude and phase .linevert split.Z.sub.2 .linevert split.<phi.sub.2)
is the complex conjugate of the bias power supply 504 output impedance. DC
bias is monitored by controller 500, which varies the bias power supply's
output power to obtain the desired measured DC bias. Controller 500
subtracts the measured value of DC bias from the desired value of DC bias.
If the difference is negative, bias power supply 504 output is increased.
If the difference is positive, bias power supply 504 output is decreased
(higher bias power supply 504 output generates a more negative DC bias).
Proportional, proportional-integral, or proportional-integral-derivative
control or other control may be used in accordance with this method.
Alternatively, instead of the preferred embodiment of adjusting bias power
supply 504 output to maintain a constant DC bias, a constant bias power
supply 504 output may be used.
Controller 500 may be a central controller, or a distributed system of
controllers.
6. Other Features
A preferred feature of the invention is to automatically vary "bottom" or
support electrode bias power to maintain a constant cathode (wafer) sheath
voltage. At low pressures (<500 mt) in a highly asymmetric system, the DC
bias measured at the cathode is a close approximation to the cathode
sheath voltage. Bottom power can be automatically varied as described in
the previous section to maintain a constant DC bias and, thus, to maintain
constant sheath voltage. Alternatively, bottom power can be used to
selectively vary DC bias and sheath voltage. Bottom power has very little
effect on plasma density and ion current density. Top electrode power has
very strong effect on plasma density and on current density, but very
small effect on cathode sheath voltage. Therefore, it is desired to use
top power to define plasma and ion current densities, and bottom power to
define cathode sheath voltage.
Features which may be incorporated in the reactor chamber system 10
include, but are not limited to, the use of a fluid heat transfer medium
to maintain the internal and/or external temperature of the gas inlet
manifold 23 above or below a certain value or within a certain range; the
use of fluid heat transfer medium to heat or cool the cathode 32C; the use
of fluid heat transfer medium to heat or cool chamber walls 12 or top 13;
resistive heating of the cathode 32C; the use of a gas heat transfer
medium between the wafer 5 and the cathode 32C; and mechanical or
electrostatic means for clamping the wafer 5 to the cathode 32C. Such
features are disclosed in commonly assigned U.S. Pat. No. 4,872,947,
issued Oct. 10, 1989, and commonly assigned U.S. Pat. No. 4,842,683,
issued Jun. 27, 1989, which are incorporated by reference.
The inventive plasma reactor system is depicted in FIG. 1 in the
conventional orientation, that is vertically, with the substrate 5
residing on an electrode 32 (cathode) and an electrode 25 located above
the electrode. For convenience, we sometimes refer here to the power
supplied to the electrode 25 as "top" power and that supplied to the
electrode/cathode 32 as "bias" or "bottom" power. These representations
and designations are for convenience only, and it is to be understood that
the described system may be inverted, that is, configured with the
electrode 32 on top and the electrode 25 located below this electrode 32,
or may be oriented in other ways, such as horizontally, without
modification. In short, the reactor system works independently of
orientation. In the inverted configuration, plasma may be generated at the
electrode 25 and transported upwardly to the substrate 5 located above the
electrode 25 in the same manner as described in the specifications. That
is, transport of active species occurs by diffusion and bulk flow, or
optionally assisted by a magnetic field having an axial gradient. This
process does not depend on gravitational forces and thus is relatively
unaffected by orientation. The inverted orientation may be useful, for
example, to minimize the probability of particles formed in the plasma
generation region in the gas phase or on a surface, falling to the
substrate. Gravity then reduces the probability of all but the smallest of
such particles moving upward against a gravitational potential gradient to
the substrate surface.
My chamber design is useful for both high and low pressure operation. The
spacing, d, between the wafer support cathode 32C and the plane of the
electrode 25 may be tailored for both high and low pressure operation. For
example, high pressure operation at 500 millitorr -50 torr preferably uses
spacing d .ltoreq.about 5 centimeters, while for lower pressure operation
over the range <0.1 millitorr-500 millitorr, a spacing d >5 centimeters
may be preferable. The chamber may incorporate a fixed spacing d, as
shown, or may utilize variable spacing designs such as interchangeable or
telescoping upper chamber sections. The reactor system 10 is useful for
processes such as high and low pressure deposition of materials such as
silicon oxide and silicon nitride; low pressure anisotropic reactive ion
etching of materials such as silicon dioxide, silicon nitride, silicon,
polysilicon and aluminum; high pressure plasma etching of such materials;
and CVD faceting involving simultaneous deposition and etchback of such
materials, including planarization of wafer topography. These and other
processes for which reactor system 10 may be used are described in
commonly assigned U.S. Pat. application Ser. No. 07,560,530, (AMAT file
no. 151-2) now abandoned, filed on Jul. 31, 1990, in the name of Collins
et al, which Collins et al patent application is incorporated by
reference.
6. Alternative Electrode Configurations
FIG. 2 schematically depicts an alternative system 120 which is similar to
the system 10, FIG. 1, except that a flat dielectric window 17P, instead
of the dome 17, is formed in the top of the enclosure, and a flat high
frequency electrode 25P (preferably formed on top of the window 17P) is
used in place of the circular electrode 25. The FIG. 2 arrangement
operates similarly to that of FIG. 1, except that the electric field is
not so confined and is perpendicular to the plane of the wafer 5. As a
result, the system 120 does not provide the damage suppression
characteristics of system 10 (that is, does not suppress wafer damage to
the same extent as system 10).
FIG. 3 depicts a system 130 which is the converse or reverse of system 120
in that the top electrode 25P is connected to the chamber wall and the
enclosure is connected to the low frequency power.
FIG. 4 depicts a system 140 which does not use a top electrode. Instead,
both the low frequency and the high frequency sources are connected to the
wafer support electrode 32. The differences occasioned by this mixed
frequency arrangement relative to system 10, FIG. 1 are, first, HF and LF
power are used to control density and energy, respectively, using a single
electrode, and, second, this arrangement does not provide the damage
suppression characteristics of system 10 (that is, does not suppress
damage to the extent of system 10).
The matching network 28 described above is preferred for satisfying the
requirements imposed by the high frequency, differential drive,
ungrounded, balanced split electrode arrangement. Also, the transmission
line structure 32 and associated matching network 43 are preferred
approaches. More generally, conventional transmission line structures and
match networks can be used, in particular for the low frequency
connections.
7. Apparatus Examples
A present working embodiment of my system incorporates the domed
configuration and the split electrode configuration depicted in FIG. 1.
The short quartz bell jar chamber 17 has a diameter of 10 inches. The
10.2-inch diameter, two-inch height electrode 25 is ungrounded and
surrounds the domed processing chamber 16A. Reflector box 44 is of
aluminum. Operation using high frequency RF energy of 1 kilowatt, 200 MHz
provides a plasma which extends about 4 inches downstream (i.e., below)
the top electrode to the wafer. This provides a plasma density of
1-2.times.10.sup.12 /cm.sup.3 and ion saturation current density of 10-15
mA/cm.sup.2 downstream at the wafer. A low frequency auxiliary bias of
13.56 MHz, 200 watts applied to a 5-inch wafer positioned on the support
electrode approximately 4 inches below (downstream) of the top electrode
provides a 200 volt cathode sheath voltage.
8. Process Examples
The above-described reactor embodying my present invention is uniquely
useful for numerous plasma processes such as reactive ion etching (RIE),
high pressure plasma etching, low pressure chemical vapor deposition (CVD)
including sputter facet deposition and planarization, and high pressure
conformal isotropic CVD. Other applications include, but are not limited
to, sputter etching, ion beam etching, or as an electron, ion or active
neutral plasma source.
RIE and low pressure CVD typically use pressures of up to 500 mt
(millitorr). High pressure plasma etch and high pressure conformal
isotropic CVD processes may be carried out at pressures from about 500 mt
to about 50 torr.
(a) Reactive Ion Etching (RIE)
In accordance with my invention, silicon oxide, silicon (single crystal
silicon), polysilicon (polycrystalline silicon), aluminum and other
materials can be etched in an RIE mode. For this purpose, the high
frequency em (electromagnetic) energy is coupled to the plasma by the top
electrode 25. Typically, relatively lower frequency AC energy is applied
to the cathode 32 (the wafer support electrode or cathode). The high
frequency top electrode power is selected to obtain the desired plasma and
ion flux density, and the lower frequency AC bias power is selected to
independently control the desired cathode sheath voltage and, thus, the
ion energy. Please note, in low pressure applications, that is, those
involving pressures within the approximate range 0.1-500 millitorr, the
cathode or wafer sheath voltage closely approximates the DC bias of the
cathode and, as a consequence, bias voltage measurements may be used to
monitor the cathode or wafer sheath voltage values.
Typically, the useful high frequency em energy range is 50-800 MHz, the
preferred useful range 50-400 MHz and the most preferred range 50-250 MHz.
Relatively low frequency AC energy (bias energy) ranges are 10 (KHz-50
MHz, 100 KHz -30 MHz and 5-15 MHz. Unless otherwise specified, the
frequency and pressure ranges specified previously in this numbered
section apply to the process parameters specified in the RIE tables below.
The useful, preferred and most preferred ranges correspond generally to
the ranges 1, 2 and 3 in the tables.
RIE Example 1: Silicon Oxide over Polysilicon (Contact Window Hole Etch)
As a first example of the RIE of silicon oxide, consider forming contact
window holes through oxide to underlying polysilicon gates. This
application is occasioned by a multiplicity of requirements, including no
damage to the polysilicon gates or to the underlying gate oxide; no
microloading; high oxide/poly selectivity (20/1); vertical oxide etch
profile; and high oxide etch rate (typical oxide thicknesses are .gtoreq.1
micron). The high selectivity requires approximately 500 eV ion energy in
the etching plasma.
As is known to those of usual skill in the art, suitable gas chemistries
for etching contact window holes in oxide comprise fluorine as the main
etchant for providing a high etch rate, and may include carbon- and
hydrogen-containing gases for enhancing etch selectivity. Specific gases
used include CHF.sub.3, CF.sub.4, C.sub.2 F.sub.6, C.sub.4 F.sub.8,
CH.sub.4, H.sub.2, NF.sub.3, and SF.sub.6. Preferred carbon to fluorine
ratios are C/F=0.1/1-2/1 and, when hydrogen is present, the preferred
hydrogen to fluorine ratios are H/F=0.1/1-0.5/1. Argon is a preferred
inert gas dopant, because it is relatively massive and inert and, thus,
contributes to the sputter etch components of the RIE process, improving
the vertical anisotropy.
Using 1 kW, 200 MHz high frequency power ("top" power); 600 watts, 13.56
MHz auxiliary bias ("bottom" or "bias" power); 10-30 millitorr pressure;
the gas chemistry CHF.sub.3 /argon and gas flow rates 100 sccm/120 sccm
provides oxide etch rates of 5,000-7,000 Angstroms/minute with an
oxide-to-poly selectivity of 20/1.
Table 1 summarizes typical contact window etch processes which satisfy the
above-described rigid etch requirements.
RIE Example 2: Silicon Oxide over Metal (Via Hole Etch)
As a second example of RIE etching of silicon oxide, consider via hole
etching through a silicon oxide layer to an underlying aluminum conductor
layer or other metal layer. Here, the critical multiple requirements
include no damage to the underlying devices; no damage (i.e., no
sputtering) of the underlying aluminum; a vertical oxide etch profile; and
a high oxide etch rate. A suitable gas chemistry for these purposes
includes fluorine compounds and, typically, carbon. Hydrogen may be used
to improve oxide/photoresist etch selectivity. Specific gases used include
CHF.sub.3, CF.sub.4, C.sub.2 F.sub.6, C.sub.4 F.sub.8, CH.sub.4, H.sub.2,
NF.sub.3, and SF.sub.6. Preferred ratios are C/F=0.1/1-2/1 and, when H is
present, H/F=0.1/1-0.5/1. As in the previous oxide example, argon is the
preferred inert gas additive, because it is relatively massive and thus
contributes to the sputter etch (of the oxide) component of the RIE
process, improving the vertical anisotropy of the process. Also, a low
cathode sheath voltage, typically .ltoreq.300 volts, is desirable to avoid
sputtering the aluminum. Preferably, the voltage is .ltoreq.200 volts and
most preferably about 100-150 volts.
Using top power of 1.5 kVW and 200 MHz; pressure of 10-30 millitorr;
reduced bias or bottom power of about 200 watts at 13.56 MHz to provide a
200 volt cathode sheath voltage; and CHF.sub.3 /CF.sub.4 /argon gas
chemistry at flow rates of 75/75/120 sccm etches vertical-wall via holes
at a rate of 4,000-5,000 Angstroms/minute without sputtering of the
aluminum. Other chemistries may be used as known by those skilled in the
art, such as CF.sub.4, C.sub.2 F.sub.6, C.sub.4 F.sub.6, CH.sub.3,F,
CH.sub.4 which may be used in various combinations.
Table 2 discloses silicon oxide etch processes which are well suited to
etching via holes. The representative cathode bias voltages disclosed in
Table 2 provide the desired cathode sheath voltages.
RIE Example 3: Oxide Sputter Etch
Table 3 specifies typical processing parameters for effecting a third type
of non-reactive ion etch oxide etch process, oxide sputter. This process
is useful for the etchback of deposited films and removal of native oxide
on silicon using a relatively non-reactive gas, preferably argon.
RIE Example 4: Selective Polysilicon Etch (Etch Poly Gate Selectively to
Oxide)
RIE etching of polysilicon and in particular selective etching of
polysilicon with respect to oxides such as underlying oxide layers,
requires an etch process characterized by no damage (to interconnects,
gates and gate oxides); no microloading; vertical polysilicon etch
profile; a high poly/oxide etch selectivity (typically .gtoreq.30/1); and
a moderate etch rate (poly thicknesses are 2,000-5,000 Angstroms).
Referring to Table 4, suitable gas chemistries for achieving these goals
include halogen-containing gases compounds. At conventional etch
temperatures, >about 0.degree. C., chlorine or bromine chemistry is
preferred. Below about -40.degree. C., fluorine chemistry can be used.
Optionally, an inert gas(es) such as argon or helium may be added to the
gas chemistry to enhance the vertical etch anisotropy. Other dopant gases
such as oxygen may be added to improve the poly/oxide etch selectivity. As
is true of the above-described RIE etching of oxide over aluminum, a low
cathode sheath voltage (<200 volts; <100 volts; 50-100 volts); is
preferred to obtain high poly silicon/oxide etch selectivity.
The following process parameters provide a polysilicon gate-forming etch
rate of 3,000-4,000 Angstroms/minute with a 35/1 selectivity of
polysilicon/oxide: 500 watts at 200 MHz top power operated at resonance;
bottom power of 100 watts at 13.56 MHZ, providing a low cathode sheath
voltage of approximately 75 volts; pressure 10-50 millitorr; and etching
gas chemistry Cl.sub.2 /He/O.sub.2 (oxygen optional) at flow rates of 80
sccm/400 sccm/(0-4 sccm). Other chlorine sources such as BCl.sub.3 may be
used.
RIE Example 5: Aluminum Etch
Table 5 depicts the process parameters for RIE etching of aluminum which
satisfy the requirements that there be no damage to underlying devices and
no corrosion of aluminum and that the process provide a high aluminum etch
rate (typically 5,000-10,000 Angstroms/min.). Suitable gas chemistries
include chlorine- and bromine-containing gases, alone or in combination.
Relatively non-reactive/inert gases such as argon may be added for the
purpose of profile control. To minimize corrosion of aluminum after etch
by chlorinated species, a photoresist strip and Al fluorine passivation
can be performed in the same or another chamber.
RIE Example 6: Single Crystal Silicon Etch
Table 6 depicts the representative proven parameters for RIE etching of
single crystal silicon in accordance with the process requirements that
there be no damage (lattice damage results from high energy bombardment in
conventional RF systems) and that the process provide a vertical silicon
etch profile, i.e., a high aspect ratio (1/w). The gas chemistry includes
halogen species and preferably both bromine and fluorine species (e.g.,
HBr+SiF.sub.4 or HBr+SiF.sub.4 +NF.sub.3) for profile control as well as
dopants such as helium and oxygen, also for profile control (HBr/SiF.sub.4
/NF.sub.3 /O.sub.2 /He).
RIE Example 7: Tungsten Etch
Table 7 discloses the process parameters for RIE etching tungsten without
damage to underlying devices. The process is based upon a gas chemistry
which comprises a fluorine-containing gas such as NF.sub.3 or SF.sub.6
and, optionally, inert gas such as argon for the purpose of increasing the
sputter etch component.
RIE Example 8: Anisotropic Photoresist Etch
Anisotropic RIE etching of photoresist may be used, for example, for
patterning resist for advanced devices. Process requirements are vertical
etch profile and no damage to underlying devices. Table 8 discloses the
parameters for anisotropic patterning of photoresist using RIE. The
associated gas chemistry comprises oxygen and, optionally,
fluorine-containing gas such as CF.sub.4, C.sub.2 F.sub.6, NF.sub.3 and/or
SF.sub.6. The wafer is maintained at a low temperature, preferably
<125.degree. C., and most preferably <75.degree. C., to avoid photoresist
reticulation. As discussed previously in the apparatus disclosure, fluid
cooling of the wafer support electrode/cathode/pedestal can be used to
provide the necessary temperature control.
Anisotropic profiles are etched in photoresist using top power of 1 kW at
200 MHz; pressure of 10-30 millitorr; gas chemistry and associated flow
rates of 30-100 sccm O.sub.2 and 10-50 sccm CF.sub.4 (optional); a bottom
bias of 0-200 watts at 13.56 MHz; and a cathode temperature of about 60
degrees C. The process provides an anisotropic photoresist etch rate of
0.8-3 micrometers/minute.
RIE Example 9: Barrier Layer Etching
Barrier layers of material such as titanium, tungsten or titanium nitride
are thin layers formed between layers of material such as oxide and
aluminum. For example, barrier layers can be used to prevent
damage/etching of aluminum during the formation of via holes in overlying
oxide layers. The barrier layer must be removed after the oxide via etch
and prior to filling the via to permit proper ohmic contact to the
aluminum. The critical features of such a barrier layer etch process
include no damage to underlying layers or devices, for example, by
sputtering the underlying aluminum. Table 9 discloses the process
parameters for a halogen-based gas chemistry comprising
chlorine-containing and fluorine-containing constituents.
b) Light Etch
A so-called light oxide etching is used after a main oxide etch step, to
remove damaged thin layers of material such as oxide or polysilicon,
without incurring additional damage. My light etch satisfies the
requirements of removing damaged removal without additional damage in part
by providing downstream etching (at the wafer support electrode/cathode)
using low bombardment energies. Table 10 shows a suitable light oxide etch
process which uses fluorine-containing gas chemistry. The light oxide etch
process of Table 10 can be changed to a light etch process for polysilicon
by substituting a chlorine-containing constituent gas such as Cl.sub.2 for
the fluorine-containing gas.
In one specific example, top power of 200-1,000 watts at 200 MHz; no bias
or bottom power; 10-50 millitorr pressure; and 30-120 sccm CF.sub.4
provides a low energy oxide etch rate of 100-1,000 Angstroms/minute.
c) High Pressure Plasma Etch
In accordance with my invention, silicon oxide, polysilicon, photoresist
and other materials can be etched in a high pressure plasma etch mode.
Certain basic features and operation are as described above in the first
paragraph under the section 11 heading. Specifically, the high frequency
em energy is coupled to the plasma by the substantially closed loop top
electrode. Relatively lower frequency AC energy may be applied to the
cathode (the wafer support electrode/cathode) as required. The high
frequency top power is selected to obtain the desired ion flux density and
the lower frequency AC bias power is selected to independently obtain and
control the desired cathode sheath voltage and, thus, ion energy.
Profile control is possible during the high pressure etch by selecting the
bias power and pressure as follows. At high pressure (1-50 torr) and low
bias power (0-200 W), the process may be isotropic or semi-anisotropic
horizontally. By increasing the bias power (200 W-1,000 W) and/or
decreasing the pressure (500 mt-1 torr), the etch process may be
semi-anisotropic vertically or anisotropic vertically. In general,
increasing/decreasing bias power increases/decreases vertical anisotropy,
while decreasing/increasing the pressure increases/decreases vertical
anisotropy. Typically, useful top and bias frequencies are, respectively,
50-800 MHz and 10 KHz-50 MHz, while more preferred useful ranges are
50-400 MHz and 100 KHz-30 MHz, and presently the most preferred ranges are
50-250 MHz and 5-15 MHz.
High Pressure Plasma Etch: Isotropic Oxide Etch
FIG. 6 depicts the structure which exists after contact or via holes 601
are etched through an oxide layer 603 to underlying conductor 602 using
the photoresist pattern definition mask 604. As integrated circuit devices
become increasingly small and features such as the via holes 601 become
correspondingly narrower, filling the hole becomes increasingly difficult.
Referring to FIG. 7, the aluminum fill is made easier by first widening
the top of the hole, as indicated at 606, FIG. 7. The widening step
requires an etch process that has a horizontal etch component. In
addition, it is desirable that this etch step not damage the integrated
circuit components. My process described in Table 11 satisfies these
requirements and, thus, is ideally suited to the application depicted in
FIG. 7 as well as to other applications requiring directional control.
Furthermore, as alluded to above, bias power and pressure may be selected
to vary the etch directionality from preferentially horizontal using
relatively high pressure (3-50 torr) with no bias or very low bias, to
isotropic at moderate pressure (1-3 torr) and no to low bias (0-200 W), to
preferentially vertical at lower pressure (500 mt-1 torr) and higher bias
(200-1,000 W). As indicated in Table 11 wafer temperatures are maintained
below 125.degree. C. for the purpose of preventing photoresist
reticulation and the resultant loss of pattern definition.
Using top power of 1-1.5 kW at 200 MHz; pressure of about 1 torr; 500
sccm-2,000 sccm NF.sub.3 or CF.sub.4 ; and a cathode temperature of about
60-75 degrees C. provides an isotropic silicon oxide etch rate of about
2,500-4,500 Angstroms/minute.
Photoresist Strip
Stripping thick photoresist masks requires high photoresist etch rates
without damage to associated integrated circuit components and without
etch residue. A downstream process is preferred. Table 12 depicts a
suitable process which is based upon a gas chemistry comprising oxygen as
the main photoresist etchant and, optionally, including nitrogen for the
purpose of increasing strip rate and/or preferably fluorine-containing gas
for passivation (of aluminum). The wafer temperature is controlled to
below 300.degree. C. for the purpose of avoiding resist reticulation. In
addition, the third example (range 3) in the table effects fluorine
passivation.
A fast downstream photoresist strip process uses top power of 1-1.5 kW at
200 MHz; (no bias or bottom power); pressure of about 1 torr; etching gas
chemistry and flow rates of 800-1,000 sccm O.sub.2, 100-200 sccm N.sub.2
(optional) and 0-100 sccm CF.sub.4 (optional); and a cathode temperature
of 100-200 degrees C. (the strip rate is temperature dependent) and
provides a strip rate of 1-3 micrometers per minute.
14. Chemical Vapor Deposition (CVD)
In accordance with my invention, low pessure chemical vapor deposition
(LPCVD) may be used to deposit various materials including silicon oxide,
boron- and phosphorous-doped oxide (including borosilicate glass (BSG),
phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG)) and
plasma nitride. The top electrode, bias electrode and pressure ranges for
effecting CVD (chemical vapor deposition) are similar to those used for
the above-described RIE etching processes. That is, the high frequency em
energy coupled to the plasma has a useful frequency range 50-800 MHz,
preferred useful range 50-400 MHz, and presently preferred range 50-250
MHz. The relatively lower frequency AC energy is applied when required to
the wafer support electrode/cathode using ranges of 10 KHz-50 MHz, 100
KHz-30 MHz and 5-15 MHz. The high frequency top power is selected to
obtain the desired ion flux density and the lower frequency AC bias power
is selected to independently obtain and control the desired cathode sheath
voltage and, thus, ion energy. Preferably, pressure is in the range
0.1-500 mt and, more preferably, 1-100 mt.
Also in accordance with my invention, high pressure chemical vapor
deposition (HPCVD) may be used to deposit various materials including
those discussed in the previous paragraph using the high frequency top
energy and the low frequency bias energy described in the preceding
paragraph, but typically using pressure >500 millitorr.
In the HPCVD application, the high frequency em energy is coupled to the
plasma by the top electrode and the relatively lower frequency AC energy
is applied to the wafer support electrode. As mentioned, the high
frequency power is selected to obtain the desired plasma density and the
lower frequency AC bias power is selected to independently obtain and
control the desired cathode sheath voltage and thus ion energy. For HPCVD
processes, both radical and ion flux densities are important. The high
pressure is used to vary the ratio of the radical deposition component to
the ion deposition component. Relatively higher pressure (5-50 mt) and
lower bias (0-200 mt) generate more radicals with respect to ions and
lower bias yields less ion directionality. Relatively lower pressures of
about 500 mt-5 torr and higher biases generate less radicals with respect
to ions, and higher bias of about 200-1,000 W yields more ion
directionality. By controlling these parameters, the degree of deposited
film conformality can be varied, from slightly preferentially horizontal
under conditions of high pressure, no bias; to isotropic using very low
bias to no bias, moderate pressure; to preferentially vertically at lower
pressure, higher bias. Preferentially horizontal pressure 10-50 torr, no
bias; isotropic pressure 5-10 torr, bias 0-200 W; and preferentially
vertical pressure 500 mt-5 torr, bias 200-1,000 W.
(a) Low Pressure CVD
1) Plasma Nitrides and Plasma Oxynitrides
Applications of plasma nitride and plasma oxynitride include as passivation
layers and intermetal dielectrics. In such applications, the associated
deposition process must not damage devices. When used to form passivation
layers, the process must provide good moisture barrier with stress control
and when used to deposit an intermetal dielectric, it must provide step
coverage, high dielectric strength, controlled physical properties
(stress), electrical properties (dielectric strength and dielectric
constant), optical properties (absorption spectrum) and chemical
properties (hydrogen content). Please note, typically plasma nitride and
plasma oxynitride are not stoichiometric; rather, the deposited nitride
materials are Si-H-N and the oxynitride materials are Si-H-O-N.
Typically, the gas chemistry comprises silane and nitrogen when low
hydrogen content nitride is required, or silane, nitrogen and ammonia
where higher hydrogen content can be tolerated, or the same considerations
apply to oxynitride except that the gas chemistry includes an
oxygen-containing gas such as nitrous oxide or oxygen itself, and
typically a lower nitrogen flow rate. The corresponding processes for
plasma nitride deposition and for plasma oxynitride deposition are
summarized below, respectively, in Tables 13 and 14.
2) LPCVD Oxide
Applications for LPCVD silicon oxide include intermetal dielectrics.
Critical process requirements include no damage to underlying devices,
gap-filling capability, high rate deposition and control of physical,
electrical, optical and chemical properties, as described in greater
detail above with respect to LPCVD plasma nitride. Typically, the gas
chemistry for the process includes a silicon-containing gas (such as
silane or TEOS), an oxygen-containing gas (oxygen itself or nitrous oxide)
and, optionally, an inert gas (typically, argon). Additional boron and
phosphorous dopants may be used to provide BSG, PSG and BPSG glasses, and
arsenic dopant may be added for the purpose of, for example, improving
step coverage The relevant process is summarized in Table 15.
One variation on the above LPCVD oxide process is bias sputter deposition,
which is a two-step process. First, the process of Table 15 is used, but
with no bottom bias, to deposit a thin oxide layer while ensuring that the
aluminum is not sputtered. Second, bottom bias and argon flow are added as
indicated in Table 15 to effect sputter facet deposition.
In a third variation, silicon oxide planarization may be effected by
modifying the bias sputter deposition process so that the ratio of
unbiased deposition rate to sputter etch rate is selected to planarize the
wafer topography. The sputter etch rate is determined by the bias and
pressure while the unbiased deposition rate is determined by the top power
and the reactant species. Consequently, the ratio is determined by
selecting the four factors, bias power, pressure, top power and reactant
flow rates.
In a fourth variation, the silicon oxide planarization can be extended to
provide a global or large area planarization process by incorporating
materials such as B.sub.2 O.sub.3 which readily flows during the
deposition process and fill large areas between features. For the
exemplary B.sub.2 O.sub.3, the associated gas chemistry is TMB
(trimethylborate) and O.sub.2 (optional inert gas (He)).
3) CVD Low Pressure (Facet) Deposition
In this process, sometimes known as a CVD facet process, etching of the
materials (e.g., oxide or nitride) deposited on the outside (upper)
corners of a trench in the silicon wafer is also carried out
simultaneously with the deposition of oxide or nitride into the trench to
avoid formation of voids in the filler material. In the prior art, such
faceting and deposition was carried out simultaneously in ECR/microwave
frequency plasma CVD. The prior art use of plasma-assisted CVD at high
frequencies, such as 13.56 MHz, resulted in the need for cycling the wafer
between a deposition chamber and an etching chamber to achieve the desired
faceting.
In accordance with my invention, simultaneous low pressure CVD deposition
and faceting may be carried out using a plasma-assisted CVD process
wherein the plasma is energized by the top electrode operating in a
frequency range of about 50 MHz to 800 MHz and, preferably, in a frequency
range of from about 50 MHz up to about 250 MHz. Wafer bias is applied to
effect sputter faceting. The use of complicated microwave/ECR equipment,
and the need for cycling the wafer between deposition and etching
chambers, are avoided.
Additionally, planarization of the wafer topography may be performed by
selecting the ratio of unbiased deposition rate to sputter etch rate based
on device/feature geometry. It may be combined with deposition of such
materials as B.sub.2 O.sub.3 which flow during the deposition process to
globally planarize the wafer.
(b) High Pressure CVD
1) Conformal Isotropic Plasma Nitride And Plasma Oxynitride
Like their LPCVD counterparts, my high pressure CVD, conformal, isotropic
plasma nitride and oxynitride processes have application such as to
passivation layers and intermetal dielectrics. The requirements and gas
chemistries discussed above relative to their LPCVD counterparts apply
here as well. In the HPCVD process, bias power is used to control film
density and stress. The processes for depositing low hydrogen nitride
(SiH.sub.4 +N.sub.2) and conventional higher hydrogen plasma nitride
(silane+nitride+ammonia) are summarized in Table P.
Table 16 can be used for the deposition of low hydrogen content oxynitride
and higher hydrogen content oxynitride by incorporating an oxygen source
(oxygen or, preferably, nitrous oxygen) in the gas chemistry. The same
N.sub.2 flow rates are used for oxynitride and nitride.
2) Conformal Isotropic Silicon Oxide
The applications and associated requirements for this HPCVD process are
similar to those for the LPCVD counterpart, with the possible exception
that the LPCVD process is more suitable to filling gaps the HPCVD process
may be favored for step coverage applications. My present HPCVD process
uses a gas chemistry comprising silicon-containing species (typically,
silane or TEOS (tetraethylorthosilicate or tetraethyloxysilicate)), an
oxygen-containing species (typically, oxygen itself or preferably nitrous
oxide) and, optionally, an inert gas (typically, argon). The overall HPCVD
process for depositing conformal silicon oxide is summarized in Table 17.
The above examples are representative. Those of usual skill in the art will
readily extend the examples to achieve isotropic and anisotropic etching
of various materials.
TABLE 1
______________________________________
OXIDE CONTACT WINDOW ETCH
OXIDE/POLY
Range
Parameter 1 2 3
______________________________________
Top elect.
300-5000 500-2500 800-2000
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power
100-1000 200-1000 400-800
(W)
Bias freq.
10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500 1-100 5-50
Wafer temp.
.ltoreq.125 -- --
(.degree.C)
Gas Chemistry
(sccm)
Etchant CF = 0.1/1-2/1
CHF.sub.3 = 30-600
50-300
Dopant HF = 0.1/1-0.5/1
Ar = 30-600 50-300
______________________________________
TABLE 2
______________________________________
OXIDE VIA HOLE ETCH
OXIDE/ALUMINUM
Range
Parameter 1 2 3
______________________________________
Top elect. 100-5000 300-2500 800-2000
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 100-1000 100-500 100-300
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Cathode .ltoreq.300 .ltoreq.200
5-50
Sheath (V)
Press. (mt)
.ltoreq.500 1-100 5-50
Wafer temp.
.ltoreq.125 -- --
(.degree.C.)
Gas Chemistry
(sccm)
Etch CF = 0.1/1-2/1
CHF.sub.3
50-300
HF = 0.1/1-0.5/1
CF.sub.4 50-300
Ar 50-300
______________________________________
TABLE 3
______________________________________
OXIDE SPUTTER ETCH
Range
Parameter 1 2 3
______________________________________
Top elect. 300-5000 500-2500 800-2000
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 0-1000 100-800 100-300
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500 1-100 1-30
Wafer temp.
-- -- --
(.degree.C.)
Gas Chemistry
(sccm)
Etchant Non-reactive Ar Ar
______________________________________
TABLE 4
______________________________________
POLY/OXIDE
Range
Parameter 1 2 3
______________________________________
Top elect. 200-1500 300-1000 300-750
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 0-500 0-300 0-200
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Cathode .ltoreq.200
.ltoreq.100
50-100
Sheath (V)
Press. (mt) .ltoreq.500
1-100 5-50
Wafer temp.
(1) >-40.degree. C.
(.degree.C.)
(2) <-40.degree. C.
Gas Chemistry
(sccm)
Etch (1) Cl or Br Cl.sub.2 or HBr or
Cl.sub.2
50-300
BCL.sub.3 + Ar
He 50-300
O.sub.2
0-20
(2) F SF.sub.6 or NF.sub.3 +
SF.sub.6
30-300
Argon Ar 30-300
______________________________________
TABLE 5
______________________________________
RIE ALUMINUM
Range
Parameter 1 2 3
______________________________________
Top elect. 500-1500 600-800 600-800
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 100-400 100-200 100-200
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500 1-100 5-50
Wafer temp.
.ltoreq.125 --
(.degree.C.)
Gas Chemistry
(sccm)
Etch Cl.sub.2 /BCl.sub.3
Cl.sub.2 + BCl.sub.3
Cl.sub.2 = 30-100
BCl.sub.3 = 30-100
Dopant BBr.sub.3
______________________________________
TABLE 6
______________________________________
RIE SILICON
Range
Parameter 1 2 3
______________________________________
Top elect.
100-2500 300-700 300-700
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power
0-500 50-200 50-150
(W)
Bias freq.
10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500
5-50 5-50
Wafer temp.
.ltoreq.125
.ltoreq.100 .ltoreq.75
(.degree.C.)
Gas Chemistry
(sccm)
Etchant Halogen HBr/SiF.sub.4 /NF.sub.3
HBr 30-100
SiF.sub.4
0-20
HBr 0-10
Dopant He/O.sub.2 O.sub.2
0-10
NF.sub.3
0-20
______________________________________
TABLE 7
______________________________________
RIE TUNGSTEN
Range
Parameter 1 2
______________________________________
Top elect. 100-2500 200-500
power (W)
Top 50-800 50-250
freq. (MHz)
Bias power 0-500 0-200
(W)
Bias freq. 10 KHz- 5 MHz-
50 MHz 15 MHz
Press. (mt) .ltoreq.500 10-100
Wafer temp. -- --
(.degree.C.)
Gas Chemistry
(sccm)
Etchant F NF.sub.3
0-200
SF.sub.6
0-200
Dopant Inert Ar 0-200
______________________________________
TABLE 8
______________________________________
ANISOTROPIC RIE PHOTORESIST
Range
Parameter 1 2 3
______________________________________
Top elect. 300-2500 300-1500 300-1500
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 0-500 0-300 0-200
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500 1-100 5-50
Wafer temp. .ltoreq.125
.ltoreq.75
(.degree.C.)
Gas Chemistry
(sccm)
Etchant O O.sub.2 10-300
Dopant F CF.sub.4 0-300
______________________________________
TABLE 9
______________________________________
RIE BARRIER LAYER
TiW/TiN
Range
Parameter 1 2 3
______________________________________
Top elect. 100-2500 300-1000 300-600
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power 0-500 0-200 100-200
(W)
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt) .ltoreq.500
1-100 5-50
Wafer temp.
(.degree.C.)
Gas Chemistry
(sccm)
Etch Halogen F + Cl CF.sub.4
0-20
BCl.sub.3
10-100
Cl.sub.2
0-20
______________________________________
TABLE 10
______________________________________
LIGHT ETCH
Range
Parameter 1 2
______________________________________
Top elect. 100-1000 100-1000
power (W)
Top 50-800 50-250
freq. (MHz)
Bias power 0-200 0-200
(W)
Bias freq. 10 KHz- 5-15 MHz
50 MHz
Press. (mt)
.ltoreq.500 5-100
Wafer temp.
-- --
(.degree.C.)
Gas Chemistry
(sccm)
Oxide F CF.sub.4
30-120
or NF.sub.3
30-120
Poly Cl Cl.sub.2
30-120
______________________________________
TABLE 11
______________________________________
HP ISOTROPIC OXIDE ETCH
Range
Parameter 1 2 3
______________________________________
Top elect.
500-5000 500-2500 500-2500
power (W)
Top 50-800 50-400 50-250
freq. (MHz)
Bias power
0-500 0-300 0-300
(W)
Bias freq.
10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
.ltoreq.500 mt
0.5-20 torr
0.5-5 torr
Wafer temp.
.ltoreq.125
.ltoreq.100
60-75
(.degree.C.)
Gas Chemistry
(sccm)
Etch F CF.sub.4 CF.sub.4
500-200
NF.sub.3 or NF.sub.3
500-200
SF.sub.6
C.sub.2 F.sub.6
______________________________________
TABLE 12
______________________________________
PHOTORESIST STRIP
Range
Parameter 1 2 3
______________________________________
Top elect. power (W)
300-5000 300-2500 300-2500
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 0-1000 0-1000
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt) 100 mt- 500-mt 500 mt-5 torr
50 torr 10 torr
Wafer temp. (.degree.C.)
.ltoreq.300
.ltoreq.250
100-200
Gas Chemistry (sccm)
Etchant O O.sub.2, N.sub.2 O
O, N.sub.2 O
500-2000
Dopant F, N CF.sub.4, NF.sub.3,
N.sub.2
0-5000
SF.sub.6, C.sub.2 F.sub.6
CF.sub.4
0-500
NF.sub.3
0-500
______________________________________
TABLE 13
______________________________________
LP PLASMA NITRIDE DEPOSITION
Parameter 1 2 3
______________________________________
Top elect. power
300-5000 300-2500 300-2500
(W)
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 0-600 0-600
Bias freq.
10 KHz-50 MHz
100 KHz-30 MHz
5-15 MHz
Press. (mt)
.ltoreq.500 .ltoreq.50 .ltoreq.50
Wafer temp. (.degree.C.)
-- 100-500 200-400
Gas Chemistry
Si & N SiH.sub.4 30-300
(sccm) N.sub.2 100-1000
NH.sub.3 0-50
______________________________________
TABLE 14
______________________________________
LP PLASMA OXYNITRIDE DEPOSITION
Parameter 1 2 3
______________________________________
Top elect. power
300-5000 300-2500 500-2500
(W)
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 0-600 0-600
Bias freq.
10 KHz-50 MHz
100 KHz-30 MHz
5-15 MHz
Press. (mt)
.ltoreq.500 .ltoreq.50 .ltoreq.50
Wafer temp. (.degree.C.)
-- 100-500 200-400
Gas Chemistry
Si SiH.sub.4 30-300
(sccm) N N.sub.2 100-1000
O O.sub.2 /N.sub.2 O
100-1000
Dopant NH.sub.3 0-50
______________________________________
TABLE 15
______________________________________
LP OXIDE DEPOSITION
Parameter 1 2 3
______________________________________
Top elect. power (W)
300-5000 500-2500 1000-2000
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 200-1000 200-1000
Bias freq. 10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt) .ltoreq.500
1-100 1-30
Wafer temp. (.degree.C.)
.ltoreq.500
200-400 300-400
Gas Chemistry (sccm)
Si SiH.sub.4 /TEOS
SiH.sub.4
30-100
O O.sub.2 /N.sub.2 O
O.sub.2
30-200
Dopant Inert Ar Ar 400-800
______________________________________
TABLE 16
______________________________________
HP OXIDE/OXYNITRIDE DEPOSITION
Parameter 1 2 3
______________________________________
Top elect. power (W)
300-5000 300-2500
500-1500
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 0-300 0-300
Bias freq. 10 KHz- 100 KHz-
5-15 MHz
50 MHz 30 MHz
Press. (mt) .gtoreq.500 500 mt- 1-10 torr
50 torr
Wafer temp. (.degree.C.)
-- 100-500 200-400
Gas Chemistry (sccm)
Nitride Si SiH.sub.4
30-100
N N.sub.2 O
400-5000
NH.sub.3
0-30
Oxynitride Si SiH.sub.4
30-100
N N.sub.2 400-5000
O N.sub.2 O
400-5000
or O.sub.2 --
NH.sub.3
0-30
______________________________________
TABLE 17
______________________________________
HP CONFORMAL OXIDE DEPOSITION
Parameter 1 2 3
______________________________________
Top elect. power
300-5000 300-2500 500-1500
(W)
Top freq. (MHz)
50-800 50-400 50-250
Bias power (W)
0-1000 0-1000 0-1000
Bias freq.
10 KHz- 100 KHz- 5-15 MHz
50 MHz 30 MHz
Press. (mt)
>500 500 mt- 500 mt-10 torr
50 torr
Wafer temp. (.degree.C.)
-- 100-500 200-400
Gas Chemistry
Si SiH.sub.4 + N.sub.2 O
30-100
+ 200-3000
(sccm) SiH.sub.4
+ N.sub.2 O
O TEOS + O.sub.2
30-100
+ 100-1000
TEOS O.sub.2
TEOS + N.sub.2 O
30-100
+ 100-1000
TEOS N.sub.2 O
______________________________________
Having thus described preferred and alternative embodiments of my system
and process those of usual skill in the art will readily adapt, modify and
extend the method and apparatus described here in a manner within the
scope of the following claims.
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